Heat exchange systems such as those found in motor vehicles include a long and complex fluid flow path in order the maximize heat transfer therethrough. A typical motor vehicle includes a radiator which comprises a metallic member having a complex, high surface area fluid flow path. The radiator is usually made from relatively thin metal and includes a number of soldered or welded joints. Vehicular cooling systems are prone to leak because of the corrosive environment and high degree of mechanical stress to which they are subject, leaks present a serious problem because they can compromise the efficiency of the heat exchanger and cause catastrophic thermal damage to the engine of the vehicle.
A number of materials have heretofore been employed for the purpose of sealing small leaks in vehicular cooling systems. These sealing compositions typically include a fine, particulate material therein which is forced, by the pressurized fluid in the cooling system through a leaking region. The particulate material is caught in, and seals, the leak. A number of vegetable root powders have been employed in stop leak compositions because they are of relatively low cost and are efficient at sealing leaking cooling systems. U.S. Pat. No. Re. 24,094 discloses a stop-leak formulation comprising an anhydrous mixture of ginger root powder dispersed in a water soluble oil. The mixture is poured into the radiator and the combination of heat and pressure disperses the oil and causes the root powder to swell and seal leaks. While this material is effective, the composition is not stable on storage, since the presence of water will cause the root powder to swell and agglomerate in the container prior to use. U.S. Pat. No. 2,935,189 discloses one approach to overcoming the problem of agglomeration. As disclosed therein, the root powder is mixed with a small amount of soluble oil and formed into pellets which are coated with an oil insoluble, water soluble polymer. The coated pellets are stored under oil. This formulation does increase shelf life somewhat, but any traces of water in the formulation will still cause deterioration and swelling of the pellets. U.S. Pat. No. 3,616,896 discloses a dual container which includes a first compartment holding a dry stop leak material and a second compartment which contains a heat exchange liquid. The contents of the two compartments are mixed just prior to use. The cost and complexity of the package has precluded widespread commercial use.
In another approach, as detailed in U.S. Pat. No. 2,935,189 employs coated pellets of solid stop leak material. These pellets are still water sensitive and have not gained commercial popularity.
In addition to the problem of water sensitivity, prior art oil-based compositions have encountered further problems. In general, consumers are adverse to placing oil-based materials into the cooling systems of their automobiles. The soluble oil can give an opaque appearance to the cooling system fluid, and can separate to generate an oil layer at the top of the fluid level. The appearance of the cooling fluid and the presence Of the oil has led consumers to the belief that the fluid, or the vehicle has been damaged and causing them to drain causing them to and flush their cooling systems and refrain from repurchase of the product. Additionally, the presence of the oil in the cooling fluid presents an environmental hazard and further complicates disposal of spent cooling fluid.
In an attempt to provide an oil-free, storage stable stop leak composition, the prior art has investigated the use of glycol-based root powder formulations. As disclosed in U.S. Pat. No. 5,282,895, the disclosure of which is incorporated herein by reference, a shelf stable aqueous stop leak formulation is comprised of root powder dispersed in a mixture of water and high-boiling glycol or glycol ether. While this formulation is fairly stable, and effective at stopping leaks, it would be desirable to find a replacement for the glycol. The glycol material is somewhat toxic, and is a particular hazard to small children and household pets because of its sweet taste. Additionally, the glycol is a relatively expensive material.
Clearly, it would be desirable to have a stop leak formulation which does not include any oil or glycols therein, but which is storage stable and not prone to freezing under normally encountered shipping and handling conditions. It is also essential that the composition not react adversely with rubber, steel, aluminum, brass, copper and other materials typically found in vehicular cooling systems. It would also be most advantageous if the material were relatively low in cost. As will be described in greater detail hereinbelow, the present invention provides a stop leak composition particularly useful for the cooling systems of motor vehicles. The stop leak composition includes no oil, glycol or ethers. It is freeze protected and storage stable and of low cost and toxicity. These and other advantages of the present invention will be readily apparent from the discussion and description which follow.